1. Field of Invention
This invention relates to a magnetic oxygen analyzer for measuring the oxygen concentration of a mixed gas flowing, for example, in a flue, wherein the analyzer provides provides improved signal to noise ratio, improves controllability of thermomagnetic winds, increases immunity to effects of ambient temperature variations, and eliminates need for precise temperature control.
2. Description of the Prior Art
Precise measurement of oxygen concentration of a mixed gas is important for a broad range of processes. Accordingly, in the art, various devices have been devised to effect such measurement; however, much remains to be improved upon.
FIG. 1(A) shows a detector used in the art in a magnetic oxygen analyzer, wherein devices 1a and 1b generate magnetic fields (e.g. permanent magnets), the ends thereof having a specific area and the magnets thereof being oppositely arranged with a specific distance therebetween; thermistors 2a and 2b produce thermomagnetic wind (hereinafter referred to as xe2x80x9cmagnetic windxe2x80x9d) and are arranged in an area where the intensity of magnetic field is caused to vary; and thermistors 3a and 3b are arranged to be external to but close to thermistors 2a and 2b and function to detect magnetic wind. When the magnetic oxygen analyzer of FIG. 1(A) is placed in a mixed gas containing oxygen, the oxygen gas which is a paramagnetic material is gathered into a magnetic field by the magnetic forces. The magnetic susceptibility of the oxygen gas thus gathered is decreased as the gas is heated by thermistors 2a and 2b, which act as heaters, and are arranged in an area having variable intensities of magnetic fields. Hence, a difference occurs between the magnetic susceptibility of the oxygen gas and that of an oxygen gas near the middle of the magnetic field. Accordingly, different magnetic forces act upon the heated and non-heated parts of the oxygen gas, and cause the forces on the different parts to be unbalanced.
There are various ways to arrange devices for generating magnetic fields and for heating. In the device of FIG. 1(A), an oxygen gas, with a greater magnetic susceptibility and located at one edge of a magnetic field, not provided with a heater, is forced to move to a heated edge of the magnetic field. In addition, a low temperature gas is caused to flow into the unheated area with a variable magnetic field intensity from other areas. Hence, a continuous flow of gas occurs.
This gas is proportional to the oxygen concentration of the mixed gas. Hence, the temperature of the thermistor placed close to a hot thermistor is raised, as compared with the temperature thereof, and thereby varying the difference in resistances between the two thermistors.
FIG. 1(B) shows mechanism for eliminating the effects of ambient temperature on the arrangement of FIG. 1(B), by controlling the temperature of the oxygen sensing element. In the circuit diagram, a constant temperature bridge is formed by resistors Rc, Rd and Rs; and a bridge comprising thermistors 2a, 2b, 3a and 3b, and resistors Ra and Rb. A variable resistor Rt is used for bridge temperature control. An amplifier 4 detects an electrical imbalance, if any, between contacts X and y, and drives a series connected transistor 5 to cancel the imbalance by changing the bridge current.
In the above arrangement, two pairs of a heat generating element and a heat sensing element are provided in the area with a variable magnetic field intensity. Hence, it is possible to reduce detection errors even when the magnetic oxygen analyzer is installed in a tilted position.
The resistance and temperature coefficient, also known as the B constant, of the thermistors varies from thermistor to thermistor. Accordingly, the resistance of thermistors 2a, 2b, 3a and 3b will vary at different rates of change according to ambient temperature variations. Thus, the output voltage that developes across the output terminals of the bridge circuit will have different temperature coefficients, depending on the combination of thermistors used. Thus, the detector, including the thermistors, require strict temperature control. This results in a problem with conventional analyzers, namely, such conventional analyzers will require a large scale, precise thermostatic chamber. Other problems with conventional magnetic oxygen analyzers are that the bandwidth of noise is comparatively wide, and that such conventional device use DC detection methods. Thus, the signal to noise ratio (S/N) is poor.
Accordingly, it can be understood that the prior art can be considerably improved upon.
An object of the invention is to overcome the aformentioned problems, deficiencies, and disadvantages of the prior art.
The invention provides a magnetic oxygen analyzer having a detector comprising a magnetic pole from oppositely arranged magnetic poles, heat generation means arranged in an area of non-uniform magnetic fields, where the intensity of a magnetic field produced by the magnetic pole is caused to vary, and a magnetic wind sensor disposed in a position whereat the sensor is not affected by heat produced by the heat generation means. A resistance change in the magnetic wind sensor, caused by change in the strength of the magnetic wind, is detected as the oxygen concentration in the mixed gas. The magnetic wind occurs by the magnetic field produced by the pole being heated by the heat generation means with the mixed gas being exposed to the analyzer and the magnetic wind then is exposed to the magnetic wind sensor.
Accordingly, the magnetic oxygen analyzer of the invention makes it possible to produce a higher volume of magnetic wind, reduce the noise bandwidth, and thereby improve the S/N ratio, and eliminate the need for precise temperature control.